The primary goal of Project M[superscript 2] was to develop and field-test challenging geometry and measurement units for all K-2 students. This article reports on the achievement results for students in Grade 2 at 12 urban and suburban sites in 4 states using the Iowa Tests of Basic Skills (ITBS) mathematics concepts subtest and an open-response assessment. The experimental group exhibited a deeper understanding of geometry and measurement concepts as measured by the open-response assessment while still performing as well on a traditional measure covering all mathematics content.